Sleeve molding

ABSTRACT

Sleeve molding apparatus and methods for making multi-layer injection molded plastic articles in successive mold cavities. In a first molding step, an inner sleeve is molded on a core in a first mold cavity, which may comprise a full body length sleeve or only a partial sleeve, such as an upper neck finish portion. The sleeve and core are withdrawn from the first mold cavity while the sleeve is still warm, and transferred without substantial delay to a second mold cavity for injection molding an outer layer which bonds to the inner sleeve. By transferring the sleeve at an elevated temperature into the second mold cavity, an improved bond is formed between the inner sleeve and outer layer which resists separation during a later reheat stretch blow molding step, and/or in use of the resulting article. In a preferred embodiment, a pasteurizable beer container is provided having a finish-only sleeve of a PEN polymer. In a second embodiment, a returnable and refillable water container is provided having a full-length body sleeve of a PEN polymer. A multi-station injection molding apparatus is provided having a transfer mechanism, such as a rotatable turret or reciprocating shuttle, for cost-effective manufacture of preforms simultaneously in multiple cavity sets.

RELATED APPLICATIONS

[0001] This is a continuation-in-part of copending and commonly ownedU.S. Ser. No. 08/534,126 filed Sep. 26, 1995, entitled “PREFORM ANDCONTAINER WITH CRYSTALLIZED NECK FINISH AND METHOD OF MAKING THE SAME,”by Wayne N. Collette and Suppayan M. Krishnakumar, which in turn is acontinuation-in-part of copending and commonly owned U.S. Ser. No.08/499,570 filed Jul. 7, 1995, entitled “APPARATUS AND METHOD FOR MAKINGMULTILAYER PREFORMS,” by Suppayan M. Krishnakumar and Wayne N. Collette,both of which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

[0002] The present invention relates to a method and apparatus formaking multilayer injection-molded plastic articles such as preforms,wherein the successive molding of an inner sleeve and outer layerenables cost-effective production of multilayer preforms forpasteurizable, hot-fillable, and returnable and refillable beveragecontainers.

BACKGROUND OF THE INVENTION

[0003] There is described in U.S. Pat. No. 4,609,516 to Krishnakumar etal. a method for forming multilayer preforms in a single injection moldcavity. In that method, successive injections of different thermoplasticmaterials are made into the bottom of the mold cavity. The materialsflow upwardly to fill the cavity and form for example a five-layerstructure across the sidewall. This five-layer structure can be madewith either two materials (i.e., the first and third injected materialsare the same) or three materials (i.e., the first and third injectedmaterials are different). Both structures are in widespread commercialuse for beverage and other food containers.

[0004] An example of a two-material, five-layer (2M, 5L) structure hasinner, outer and core layers of virgin polyethylene terephthalate (PET),and intermediate barrier layers of ethylene vinyl alcohol (EVOH). Anexample of a three-material, five-layer (3M, 5L) structure has inner andouter layers of virgin PET, intermediate barrier layers of EVOH, and acore layer of recycled or post-consumer polyethylene terephthalate(PC-PET). Two reasons for the commercial success of these containers arethat: (1) the amount of relatively expensive barrier material (e.g.,EVOH) can be minimized by providing very thin intermediate layers; and(2) the container resists delamination of the layers without the use ofadhesives to bond the dissimilar materials. Also, by utilizing PC-PET inthe core layer, the cost of each container can be reduced without asignificant change in performance.

[0005] Although the above five-layer, and other three-layer (see forexample U.S. Pat. No. 4,923,723) structures work well for a variety ofcontainers, as additional high-performance and expensive materialsbecome available there is an on-going need for processes which enableclose control over the amount of materials used in a given containerstructure. For example, polyethylene naphthalate (PEN) is a desirablepolyester for use in blow-molded containers. PEN has an oxygen barriercapability about five times that of PET, and a higher heat stabilitytemperature—about 250° F. (120° C.) for PEN, compared to about 175° F.(80° C.) for PET. These properties make PEN useful for the storage ofoxygen-sensitive products (e.g., food, cosmetics, and pharmaceuticals),and/or for use in containers subject to high temperatures (e.g., refillor hot-fill containers). However, PEN is substantially more expensivethan PET and has different processing requirements: Thus, at present thecommercial use of PEN is limited.

[0006] Another high-temperature application is pasteurization—apasteurizable container is filled and sealed at room temperature, andthen exposed to an elevated temperature bath for about ten minutes orlonger. The pasteurization process initially imposes high temperaturesand positive internal pressures, followed by a cooling process whichcreates a vacuum in the container. Throughout these procedures, thesealed container must resist deformation so as to remain acceptable inappearance, within a designated volume tolerance, and without leakage.In particular, the threaded neck finish must resist deformation whichwould prevent a complete seal.

[0007] A number of methods have been proposed for strengthening the neckfinish. One approach is to add an additional manufacturing step wherebythe neck finish, of the preform or container, is exposed to a heatingelement and thermally crystallized. However, this creates severalproblems. During crystallization, the polymer density increases, whichproduces a volume decrease; therefore, in order to obtain a desired neckfinish dimension, the as-molded dimension must be larger than the final(crystallized) dimension. It is thus difficult to achieve closedimensional tolerances and, in general, the variability of the criticalneck finish dimensions after crystallization are approximately twicethat prior to crystallization. Another detriment is the increased costof the additional processing step, as it requires both time and theapplication of energy (heat). The cost of producing a container is veryimportant because of competitive pressures and is tightly controlled.

[0008] An alternative method of strengthening the neck finish is tocrystallize select portions thereof, such as the top sealing surface andflange. Again, this requires an additional heating step. Anotheralternative is to use a high T_(g) material in one or more layers of theneck finish. This also involves more complex injection moldingprocedures and apparatus.

[0009] Thus, it would be desirable to provide an injection-moldedarticle such as a preform which incorporates certain high-performancematerials, and a commercially acceptable method of manufacturing thesame.

SUMMARY OF THE INVENTION

[0010] The present invention is directed to a method and apparatus formaking a multilayer injection-molded plastic article, such as a preform,which is both cost-effective and enables control over the amounts ofmaterials used in the various layers and/or portions of the article.

[0011] According to a method/embodiment of the invention, an innersleeve is molded on a first core positioned in a first mold cavity. Theinner sleeve is only partially cooled before being transferred whilestill at an elevated temperature to a second mold cavity where an outerlayer is molded over the inner sleeve. By providing the inner sleeve inthe second mold cavity at the elevated temperature, bonding between theinner sleeve and outer layer is enabled during the second molding step,such that layer separation is avoided in the final molded article. Theinner sleeve may comprise a full-length inner sleeve, extendingsubstantially the full length of the article, or alternatively maycomprise only an upper portion of the article, in which case the outerlayer comprises a lower portion of the article and there is someintermediate portion in which the outer layer is bonded to the innersleeve.

[0012] In one embodiment, a first thermoplastic material is used to makean inner sleeve which comprises a neck finish portion of the preform.The first thermoplastic material is preferably a thermal resistantmaterial having a relatively high T_(g), and/or forms a crystallizedneck finish during the first molding step. In contrast, a lower bodyportion of the preform is made of a second thermoplastic material havinga relatively lower thermal resistance and/or lower crystallization ratecompared to the first material, and forms a substantially amorphousbody-forming portion of the preform. In one example, by achievingcrystallization in the neck finish during the first molding step, theinitial and finish dimensions are the same so that the dimensionalvariations caused by the prior art post-molding crystallization step(and the expense thereof) are eliminated. Also, a higher average levelof crystallization can be achieved in the finish, by utilizing thehigher melt temperatures and/or elevated pressures of the moldingprocess.

[0013] In another embodiment, a full-length body sleeve is provided madeof a high-performance thermoplastic resin, such as PEN homopolymer,copolymer or blend. The PEN inner sleeve provides enhanced thermalstability and reduced flavor absorption, both of which are useful inrefill applications. The amount of PEN used is minimized by this processwhich enables production of a very thin inner sleeve layer, compared toa relatively thick outer layer (made of one or more lower-performanceresins).

[0014] Another aspect of the invention is an apparatus for thecost-effective manufacture of such preforms. The apparatus includes atleast one set of first and second molding cavities, the first moldcavity being adapted to form the inner sleeve and the second mold cavityadapted to form the outer layer. A transfer mechanism includes at leastone set of first and second cores, wherein the cores are successivelypositionable in the first and second molding cavities. In one cycle, afirst core is positioned in a first mold cavity while a first innersleeve is molded on the first core, while a second core, carrying apreviously-molded second inner sleeve, is positioned in a second moldcavity, for molding a second outer layer over the second inner sleeve.By simultaneously molding in two sets of cavities, an efficient processis provided. By molding different portions/layers of the articlesseparately in different cavities, different temperatures and/orpressures may be used to obtain different molding conditions and thusdifferent properties in the different portions/layers. For example, itis possible to mold the crystallized neck finish portion in a firstcavity, while molding a substantially amorphous outer layer in thesecond cavity.

[0015] The resulting injection-molded articles, and/or expandedinjection-molded articles, may thus have a layer structure which is notobtainable with prior processes.

[0016] The following chart provides temperature/time/pressure ranges forcertain preferred embodiments, which are described in greater detail inthe following sections:

[0017] a) for an inner sleeve of PEN polymer material and an outer layerof PET polymer material range (on the order of) first molding step: coretemperature  5-80° C. mold cavity temperature 40-120° C. melttemperature 275-310° C.  cycle time 4-8 seconds outer surfacetemperature of sleeve 60-120° C. second molding step: core temperature 5-80° C. mold cavity temperature  5-60° C. cycle time 20-50 secondspressure 8000-15,000 psi

[0018] b) for an inner sleeve of crystallized polyester material and anouter layer of PET polymer material range (on the order of) firstmolding step: core temperature  5-60° C. mold cavity temperature 80-150°C. melt temperature 270-310° C.  cycle time 5-8 seconds outer surfacetemperature of sleeve 80-140° C. second molding step: core temperature 5-60° C. mold cavity temperature  5-60° C. cycle time 20-35 secondspressure 8000-15,000 psi

[0019] The present invention will: be more particularly set forth in thefollowing detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIGS. 1A-1D are schematic illustrations of a first methodembodiment of the present invention for making a preform having afull-length inner sleeve and a single outer layer;

[0021] FIGS. 2A-2B are schematic illustrations of an injection-moldingapparatus and the sequence of operations for making a preform such asthat shown in FIG. 1D, wherein a rotary turret transfers two sets ofcores between two sets of cavities; FIG. 2A shows the cavities/cores ina closed position and FIG. 2B shows the cavities/cores in an openposition;

[0022]FIG. 3 is a time line showing the sequence of operations for themolding apparatus of FIG. 2;

[0023]FIG. 4A is a front elevational view of a returnable and refillablecontainer, partially in section, made from the preform of FIG. 1D, andFIG. 4B is an enlarged fragmentary cross-section of the containersidewall taken along the line 4B-4B of FIG. 4A;

[0024] FIGS. 5A-5D are schematic illustrations of a second methodembodiment of the present invention for making a preform having a finishonly sleeve and a multilayer outer layer;

[0025] FIGS. 6A-6D are schematic illustrations of an injection-moldingapparatus and sequence of operations for making a preform such as thatshown in FIG. 5D, wherein the transfer mechanism is a reciprocatingshuttle; FIG. 6A shows the shuttle in a first closed position in firstand second mold cavities; FIG. 6B shows the shuttle in a second openposition after retraction from the first and second mold cavities; FIG.6C shows the shuttle in a second open position beneath the second andthird mold cavities; and FIG. 6D shows the shuttle in a fourth closedposition in the second and third mold cavities;

[0026]FIG. 7 is a time line of the sequence of operations shown in FIG.6;

[0027]FIG. 8A is a cross-sectional view of a third preform embodiment ofthe present invention having a full-thickness neck sleeve and multilayerbody portion, and FIG. 8B is an enlarged fragmentary view of the neckfinish of the preform of FIG. 8A;

[0028]FIG. 9A is a front elevational view of a hot-fill container madefrom the preform of FIG. 8A, and FIG. 9B is a fragmentary cross-sectionof the container sidewall taken along line 9B-9B of FIG. 9A;

[0029]FIG. 10 is a cross-sectional view of a fourth preform embodimentof the present invention, having a full-length body sleeve andmultilayer outer layer;

[0030]FIG. 11 is a cross-sectional view of a fifth preform embodiment ofthe present invention, including a full-length body sleeve and an extraouter base layer;

[0031]FIG. 12 is a cross-sectional view of a sixth preform embodiment ofthe present invention, having a finish sleeve and a single layer outerlayer;

[0032]FIGS. 13A and 13B are graphs showing the change in meltingtemperature (MP) and orientation temperature (T_(g)) for various PEN/PETcompositions; and

[0033]FIG. 14 is a schematic illustration of a three-station reheatingapparatus, including IR heating stations A and C and RF heating stationB.

DETAILED DESCRIPTION First Preform Embodiment (Refillable Water)

[0034] FIGS. 1A-1D illustrate schematically one method embodiment formaking a preform with a full-length body sleeve and a single outerlayer; this preform is particularly useful for making a returnable andrefillable water bottle. FIG. 1A shows a first core 9 positioned in afirst mold cavity 11, and forming a chamber therebetween in which thereis formed an injection-molded inner sleeve 20. The sleeve 20 ispartially cooled and then the core 9 carrying sleeve 20 is removed fromthe first mold cavity as shown in FIG. 1B. While still warm, the sleeve20 on core 9 is inserted into a second mold cavity 12 which forms aninterior molding chamber for forming an outer layer 22 over the innersleeve 20. After the second molding step, a preform 30 has been formedincluding outer layer 22 and inner sleeve 20 as shown in FIG. 1D. Theinner sleeve includes a top flange 21 which will form the top sealingsurface of the resulting container (see FIG. 4).

[0035] The first method embodiment will now be described in greaterdetail in regard to the apparatus shown in FIGS. 2A-2B, and a timesequence of operations illustrated in the time line of FIG. 3.

[0036] As shown in FIGS. 2A-2B, a four-sided rotatable turret 2 isinterposed between a fixed platen 3 and a movable platen 4 on aninjection-molding machine. The turret 2 is mounted on a carriage 5 whichis slidable in the direction of platen motion (shown by arrows A₁ andA₂). The turret 2 is rotatable (shown by arrow A₃) about an axis 6disposed perpendicular to the direction of platen motion. The turret isrotatable into two operative positions spaced 180° apart. In each ofthese positions, the two opposing faces 7, 8 of the turret carryingfirst and second sets of cores 9, 10 respectively, are received in afirst set of cavities 11 on the movable platen 4, and a second set ofcavities 12 on the fixed platen 3. After a core set has beensuccessfully positioned in each of the mold cavities, the finishedpreforms may be ejected from the cores. Each of the mold cavity and coresets include water passages 15 for heating or cooling of thecavities/cores to achieve a desired temperature during molding.

[0037] The sequence of operations for forming a particular preform willnow be described. The preform has a full-body sleeve of a PEN polymer,such as homopolymer PEN, or a PEN/PET copolymer or blend. The preformhas a single outer layer made of virgin PET.

[0038] In FIG. 2A, the movable platen 4 carrying the first set of moldcavities 11, and the carriage 5 carrying the turret 2, are each moved onguide bars (tie rods) 13, 14 to the left towards the fixed platen 3 toclose the mold (i.e., both cavities). The first set of cores 9 on theleft face 7 of the turret are positioned in the first cavity set 11(first molding station); each first core/cavity pair defines an enclosedchamber for molding an inner sleeve about the first core. The PENpolymer is injected via nozzle 16 into the first mold cavities to formthe inner sleeve. Simultaneously, the second core set 10 (on the secondface 8 of the turret) is positioned in the second cavity set 12 (secondmolding station). Virgin PET is injected via nozzle 17 into the secondset of cavities to form a single outer layer about a previously-formedinner sleeve on each of the second cores.

[0039] Next, the mold is opened as shown in FIG. 2B by moving both themovable platen 4 and carriage 5 to the left, whereby the first cores 9are removed from the first cavity 11 and the second cores 10 are removedfrom the second cavity 12. Now, the finished preforms 30 on the secondcore set are ejected. The finished preforms 30 may be ejected into a setof robot cooling tubes (not shown) as is well known in the art. Next,the turret 2 is rotated 180°, whereby the first set of cores 9 with theinner sleeves 20 thereon are now on the right side of the turret (andready for insertion into the second set of cavities), while the secondset of (empty) cores 10 is now on the left side of the turret (ready forinsertion into the first set of mold cavities). Again, the mold isclosed as shown in FIG. 2A and injection of the polymer materials intothe first and second sets of cavities proceeds as previously described.

[0040] In this embodiment, the first and second cores are held at atemperature in a range on the order of 60-70° C., whether they arepositioned in the first mold cavities or the second mold cavities. Thefirst mold cavities (for forming the inner sleeve) are held at atemperature on the order of 85-95° C. The melt temperature of the PENpolymer is on the order of 285-295° C. The cycle time in the first moldcavity is on the order of 6-7 seconds, i.e., the time lapse between thefirst and second injections. This is because, as shown in FIG. 3, thehold and cool stage is substantially eliminated in the first moldcavities. The outer surface temperature of the sleeve (opposite theinner surface engaging the core) at the start of the second injection is100-110° C.

[0041] During the second molding step, the core temperature is again at60-70° C., but the second mold cavity temperature is 5-10° C. (muchlower than the first cavity temperature, to enable quick cooling of thepreform). The melt temperature of the virgin PET is on the order of 260to 275° C.; this is lower than the melt temperature of the PEN polymer,but because the PEN polymer is still warm (at a temperature of 100-110°C.) during the second molding step, there is melt adhesion (includingdiffusion bonding and chain entanglement) which occurs between the PENpolymer chains and virgin PET polymer chains (inner sleeve and outerlayer) respectively. The cycle time for the second molding step is onthe order of 35 to 37 seconds.

[0042]FIG. 3 is a time line with the cycle time along the x axis (timein seconds), and the sequence of steps in the second cavity set shownabove the x axis, and the sequence of steps in the first cavity setshown below the x axis. At t=0, the mold is closed (see FIG. 2A) and thepressure is built up. At t=1.5 seconds, the second cavity (for formingthe outer layer) is filled, the pressure boosted, and then the pressurereduced during the hold and cooling stage; this continues until t=33seconds in the second cavity. Meanwhile, no action is required at t=1.5seconds in the first cavity (“no action period”); rather, it is notuntil t=31 seconds that the first cavity is filled and the pressureincreased and held, until t=33 seconds. This substantial elimination ofthe hold and cooling stage (in the first cavity) produces an innersleeve which is still at an elevated temperature when it is subsequentlyis positioned in the second cavity, and enables melt adhesion betweenthe outer surface of the inner sleeve and outer layer. At t=33 seconds,the mold is opened (see FIG. 2B), and the preforms from the secondcavity are ejected. Then, at t=35 seconds, the turret 2 is rotated so asto position the still-warm sleeves (just made in the first cavity) in aposition to be inserted into the second cavity, while the now-empty coreset (previously in the second cavity) is now positioned to be insertedin the first cavity. At t=36 seconds, we are ready to begin the nextcycle.

[0043] The method and apparatus of FIG. 2 may be advantageously used toproduce multilayer preforms for a great variety of applications,including refill, hot-fill and pasteurizable containers. A number ofalternative embodiments are described below.

[0044] The preform made according to the method and apparatus of FIGS.1-3 includes a full-body inner sleeve 20 of PEN polymer, and a singleouter layer 22 of virgin PET. The preform is substantially transparentand amorphous and may be reheated and stretch blow-molded to form a 1.5liter returnable and refillable water bottle, such as that shown in FIG.4A. The container 40 is about 13.2 inches (335 mm) in height and about3.6 inches (92 mm) in widest diameter. The container body has an opentop end with a small diameter neck finish 42 having external screwthreads for receiving a screw cap (not shown), and a closed bottom endor base 48. Between the neck finish 42 and base 48 is a substantiallyvertically-disposed sidewall 45 (defined by vertical axis or centerlineCL of the bottle), including a substantially cylindrical panel portion46 and a shoulder portion 44 tapering in diameter from panel 45 to neckfinish 42. The base 48 is a champagne-style base with a central gateportion 51 and, moving radially outwardly towards the sidewall, anoutwardly concave dome 52, an inwardly concave chime 54, and a radiallyincreasing and arcuate outer base portion 56 for a smooth transition tothe sidewall panel 46. The chime 54 is a substantially toroidal-shapedarea around a standing ring (chime) on which the bottle rests.

[0045]FIG. 4B shows in cross-section the multilayer panel portion 46,which includes an inner sleeve layer 41 (an expanded version of preformsleeve 20), and an outer layer 43 (an expanded version of preform outerlayer 22). One benefit of the present invention is that the layers 41and 43 have bonded and will not separate during reheat stretch blowmolding or use of the container, in this case including the intended 20or more refill cycles. In addition, a flange 47 (same as flange 21 ofthe preform) forms a top sealing surface of the container with increasedstrength and thermal resistance.

Second Preform Embodiment (Pasteurizable Beer)

[0046] FIGS. 5A-5D illustrate schematically a second method embodimentfor making a finish-only sleeve and a multiple outer layer preform; thispreform is adapted for making a pasteurizable beer container. FIG. 5Ashows a core 207 positioned in a first mold cavity 213; together theyform a first molding chamber in which a finish-only sleeve 250 isinjection molded. FIG. 5A shows an injection nozzle 211 in the moldcavity 213, through which a molten thermoplastic material is injectedfor forming the sleeve 250. FIG. 5B shows the formed sleeve 250 on thecore 207, the sleeve having been removed from first mold cavity 213while it is still warm. The core 207 carrying the sleeve 250 is thenpositioned in a second mold cavity 214 as shown in FIG. 5C. The secondmold cavity 214 and core 207 form a second molding chamber adapted toform an outer layer 252 over the inner sleeve 250. A plurality ofdifferent thermoplastic materials are injected through a gate 209 in thebottom of the second mold cavity 214, to form the multiple outer layers.As shown in FIG. 5D, the outer layer 252 extends the full length of thepreform. A sequential injection process such as that described in U.S.Pat. No. 4,609,516 to Krishnakumar et al., may be used to form inner andouter layers 253, 254 of virgin PET, core layer 255 of recycled PET(which may include an oxygen scavenging material), and inner and outerintermediate layers 256, 257 of an oxygen barrier material, between theinner/core/outer layers. In this embodiment, only the virgin PET extendsup into the neck finish of the preform, forming a single layer 258 overinner sleeve 250. In the base of the preform, a final injection ofvirgin PET forms a plug 259 for clearing the nozzle before the nextinjection cycle.

[0047] FIGS. 6A-6D illustrate a reciprocating shuttle apparatus, insteadof the rotatable turret of FIGS. 2A-2D, which comprises a secondapparatus embodiment. This second apparatus will now be described withrespect to forming the preform of FIG. 5. FIG. 7 shows a time line ofthe sequence of operations.

[0048] The apparatus (see FIGS. 6A-6D) includes first and secondparallel guide bars 202, 203 on which a platen 205 is movably mounted inthe direction of arrow A₄. The platen 205 carries a platform or shuttle206 which is movable in a transverse direction across the platen 205 asshown by arrow A₅. A fixed platen 212 at one end of the guide bars holdsthree injection mold cavity sets 213, 214 and 215 which are supplied bynozzles 218, 219 and 220 respectively. The left (first) and right(third) cavity sets 213 and 215 are used to form neck portions ofpreforms, while the middle (second) cavity set 214 is used for moldingbody-forming portions.

[0049]FIG. 5A shows an arbitrarily-designated first step wherein thefirst core set 207 is positioned in left cavity set 213 for forming afirst set of preform neck portions (sleeves). Simultaneously, secondcore set 208 is positioned in middle cavity set 214 for molding a set ofmultilayer body-forming portions (over a second set of previously moldedneck portions). FIG. 5B shows the core sets following removal from thecavity sets, with a neck sleeve 250 on each core of core set 207, and apreform 260 on each core of core set 208. The completed preforms 260 arethen ejected from the core set 208.

[0050] In a second step (FIG. 6C), the shuttle 206 is moved to the rightsuch that the first core set 207 with neck sleeves 250 are nowpositioned below middle cavity 214, while second core set 208 with nowempty cores 216 is positioned below right cavity set 215. Movable platen205 is then moved towards fixed platen 212 so as to position first coreset 207 in middle cavity set 214, and second core set 208 in rightcavity set 215 (FIG. 6D). Again, body-forming portions are formed overthe previously formed neck sleeves in middle cavity set 214, while necksleeves are molded on each of the cores in the core set 208 in rightcavity set 215. The movable platen 205 is then retracted to remove thecore sets from the cavity sets, the finished preforms on the first coreset 207 are ejected, and the shuttle 206 returns to the left for moldingthe next set of layers.

[0051]FIG. 7 is a time line of the operations shown in FIG. 6, with timein seconds along the x axis, and the sequence of steps in the secondcavity 214 shown above the x axis, and the sequence of steps in thefirst cavity 213 shown below the x axis. First, at t=0, the mold isclosed (FIG. 6A) and the pressure builds up. Then, at t=1.5 seconds, thesecond cavity 214 is filled (forming the outer layer), the pressureincreased, and the pressure held while the preform cools, until t=21seconds. Meanwhile, no action is required in the first cavity at t=1.5seconds. at t=20 seconds, the first cavity 213 is filled with PENpolymer and the pressure increased and held until t=21 seconds (againthe hold and cooling stage has been substantially eliminated in thefirst cavity set by delaying the filling stage until near the end of thehold and cooling stage for the second cavity set). At t=21 seconds, themold is opened and the preforms 260 are ejected from the secondcavities. At t=23 seconds, the shuttle 206 with the still warm necksleeves is transferred to the second shuttle position as shown in FIG.6C, and at t=24 seconds the mold is closed as shown in FIG. 6D.

[0052] In this particular embodiment, the first and second core sets207, 208 are held at a temperature on the order of 60-70° C. during bothof the first and second molding steps. The first mold cavity (forforming the neck finish sleeve) is on the order of 75-85° C. The PENpolymer has a melt temperature on the order of 275-285° C. The cycletime in the first cavity is on the order of 5-6 seconds; this is thetime lapse between the first and second injection steps. The surfacetemperature of the sleeve at the time of the second injection is on theorder of 100-110° C.

[0053] In the second molding step, the core temperature is on the orderof 60-70° C., and the second mold cavity is at a temperature on theorder of 5-10° C. The cycle time in the second mold cavity is on theorder of 23-25 seconds. The elevated temperature at the outer surface ofthe sleeve, at the time of the second molding step, causes melt adhesion(including diffusion bonding and chain entanglement) between the PENpolymer of the sleeve and the virgin PET of the outer layer portion 258which is adjacent the sleeve 250.

Third Preform Embodiment (Hot Fill)

[0054] A further preform/container embodiment is illustrated in FIGS.8-9. FIGS. 8A-8B show a multilayer preform 330 and FIGS. 9A-9B show ahot-fill beverage bottle 370 made from the preform of FIG. 8. In thisembodiment, a first molded sleeve forms the entire thickness of the neckfinish, and is joined at its lower end to a second molded body-formingportion.

[0055]FIG. 8A shows a substantially cylindrical preform 330 (defined byvertical centerline 332) which includes an upper neck portion or finishsleeve 340 bonded to a lower body-forming portion 350. The crystallizedneck portion is a monolayer of CPET and includes an upper sealingsurface 341 which defines the open top end 342 of the preform, and anexterior surface having threads 343 and a lowermost flange 344. CPET,sold by Eastman Chemical, Kingsport, Tenn., is a polyethyleneterephthalate polymer with nucleating agents which cause the polymer tocrystallize during the injection molding process. Below the neck finish340 is a body-forming portion 350 which includes a flaredshoulder-forming section 351, increasing (radially inwardly) in wallthickness from top to bottom, a cylindrical panel-forming section 352having a substantially uniform wall thickness, and a base-formingsection 353. Body-forming section 350 is substantially amorphous and ismade of the following three layers in serial order: outer layer 354 ofvirgin PET; core layer 356 of post-consumer PET; and inner layer 358 ofvirgin PET. The virgin PET is a low copolymer having 3% comonomers(e.g., cyclohexane dimethanol (CHDM) or isophthalic acid (IPA)) by totalweight of the copolymer. A last shot of virgin PET (to clean the nozzle)forms a core layer 359 in the base.

[0056] This particular preform is designed for making a hot-fillbeverage container. In this embodiment, the preform has a height ofabout 96.3 mm, and an outer diameter in the panel-forming section 352 ofabout 26.7 mm. The total wall thickness at the panel-forming section 352is about 4 mm, and the thicknesses of the various layers are: outerlayer 354 of about 1 mm, core layer 356 of about 2 mm, and inner layer358 of about 1 mm. The panel-forming section 352 may be stretched at anaverage planar stretch ratio of about 10:1, as described hereinafter.The planar stretch ratio is the ratio of the average thickness of thepreform panel-forming portion 352 to the average thickness of thecontainer panel 383, wherein the “average” is taken along the length ofthe respective preform or container portion. For hot-fill beveragebottles of about 0.5 to 2.0 liters in volume and about 0.35 to 0.60millimeters in panel wall thickness, a preferred planar stretch ratio isabout 9 to 12, and more preferably about 10 to 11. The hoop stretch ispreferably about 3.3 to 3.8 and the axial stretch about 2.8 to 3.2. Thisproduces a container panel with the desired abuse resistance, and apreform sidewall with the desired visual transparency. The specificpanel thickness and stretch ratio selected depend on the dimensions ofthe bottle, the internal pressure, and the processing characteristics(as determined for example, by the intrinsic viscosity of the particularmaterials employed).

[0057] In order to enhance the crystallinity of the neck portion, a highinjection mold temperature is used at the first molding station. In thisembodiment, CPET resin at a melt temperature of about 280 to 290° C. isinjection molded at a mold cavity temperature of about 110 to 120° C.and a core temperature of about 5 to 15° C., and a cycle time of about 6to 7 seconds. The first core set, carrying the still warm neck portions(outer surface temperature of about 115 to 125° C.), are thentransferred to the second station where multiple second polymers areinjected to form the multilayer body-forming portions and melt adhesionoccurs between the neck and body-forming portions. The core and/orcavity set at the second station are cooled (e.g., 5 to 15° C.core/cavity temperature) in order to solidify the performs and enableremoval from the molds (cycle time of about 23 to 25 seconds) withacceptable levels of post-mold shrinkage. The cores and cavities at boththe first and second stations include water cooling/heating passages foradjusting the temperature as desired.

[0058] As used herein, “melt adhesion” between the inner sleeve andouter layer is meant to include various types of bonding which occur dueto the enhanced temperature (at the outer surface of the inner sleeve)and pressure (e.g., typical injection molding on the order of8,000-15,000 psi) during the second molding step, which may includediffusion, chemical, chain entanglement, hydrogen bonding, etc.Generally, diffusion and/or chain entanglement will be present to form abond which prevents delamination of the layers in the preform, and inthe container when filled with water at room temperature (25° C.) anddropped from a height of eighteen inches onto a thick steel plate.

[0059]FIG. 8B is an expanded view of the neck finish 340 of preform 330.The monolayer CPET neck finish is formed with a projection 345 at itslower end, which is later surrounded (interlocked) by the virgin PETmelt from the inner and outer layers 354,358 at the second moldingstation. The CPET neck finish and outermost virgin PET layers of thebody are melt adhered together in this intermediate region (between thelower end of the neck finish sleeve and the upper end of thebody-forming region).

[0060]FIG. 9A shows a unitary expanded plastic preform container 370,made from the preform of FIG. 8. The container is about 182.0 mm inheight and about 71.4 mm in (widest) diameter. This 16-oz. container isintended for use as a hot-fill non-carbonated juice container. Thecontainer has an open top end with the same crystallized neck finish 340as the preform, with external screw threads 343 for receiving a screw-oncap (not shown). Below the neck finish 340 is a substantially amorphousand transparent expanded body portion 380. The body includes asubstantially vertically-disposed sidewall 381 (defined by verticalcenterline 372 of the bottle) and base 386. The sidewall includes anupper flared shoulder portion 382 increasing in diameter to asubstantially cylindrical panel portion 383. The panel 383 has aplurality of vertically-elongated, symmetrically-disposed vacuum panels385. The vacuum panels move inwardly to alleviate the vacuum formedduring product cooling in the sealed container, and thus preventpermanent, uncontrolled deformation of the container. The base 386 is achampagne-style base having a recessed central gate portion 387 andmoving radially outwardly toward the sidewall, an outwardly concave dome388, an inwardly concave chime 389, and a radially increasing andarcuate outer base portion 390 for a smooth transition to the sidewall381.

[0061]FIG. 9B shows in cross section the multilayer panel portion 383including an outer layer 392, a core layer 394. and an inner layer 396,corresponding to the outer 354, core 356 and inner 358 layers of thepreform. The inner and outer container layers 392, 396 (of virgin PETcopolymer) are each about 0.1 mm thick, and the core layer 394 (ofpost-consumer PET) is about 0.2 mm thick. The shoulder 382 and base 386are stretched less and therefore are relatively thicker and lessoriented than the panel 383.

Fourth Preform Embodiment

[0062] A fourth preform embodiment is illustrated in FIG. 10. Amultilayer preform 130 is made from the method and apparatus of FIGS.1-2, and is adapted to be reheat stretch blow-molded into a refillablecarbonated beverage bottle similar to that shown in FIG. 4, but having athickened base area including the chime for increased resistance tocaustic and pressure induced stress cracking.

[0063] In FIG. 10 there is shown a preform 130 which includes a PENinner sleeve layer 120, and a three-layer outer layer comprisingoutermost (exterior) virgin PET layer 123, first intermediate (interior)PC-PET layer 124, and second intermediate (interior) virgin PET layer125. The inner sleeve layer 120 is continuous, having a body portion 121extending the full length of the preform and throughout the base. Thesleeve layer further includes an upper flange 122 which forms the topsealing surface of the preform. The outer layer similarly extends thefull length and throughout the bottom of the preform.

[0064] The preform 130 includes an upper neck finish 132, a flaredshoulder-forming section 134 which increases in thickness from top tobottom, a panel-forming section 136 having a uniform wall thickness, anda thickened base-forming section 138. Base section 138 includes an uppercylindrical thickened portion 133 (of greater thickness than the panelsection 136) which forms a thickened chime in the container base, and atapering lower portion 135 of reduced thickness for forming a recesseddome in the container base. A last shot of virgin PET (to clean thenozzle) forms a core layer 139 in the base. A preform having a preferredcross-section for refill applications is described in U.S. Pat. No.5,066,528 granted Nov. 19, 1991 to Krishnakumar et al., which is herebyincorporated by reference in its entirety.

[0065] This particular preform is designed for making a refillablecarbonated beverage container. The use of an inner sleeve 120 of a PENhomopolymer, copolymer, or blend provides reduced flavor absorption andincreased thermal stability for increasing the wash temperature. Theinner PEN sleeve can be made relatively thin according to the method ofFIG. 1. The interior PC-PET layer 124 can be made relatively thick toreduce the cost of the container, without significantly affectingperformance. In this example, the preform has a height of about 7.130inches (181.1 mm), and an outer diameter in the panel-forming section136 of about 1.260 inches (32.0 mm). At the panel-forming section 136,the total wall thickness is about 0.230 inches (5.84 mm), and thethicknesses of the various layers are: inner layer 120 of about 0.040inches (1.0 mm), outermost layer 123 of about 0.040 inches (1.0 mm),first intermediate layer 124 of about 0.130 inches (3.30 mm), and secondintermediate layer 125 of about 0.020 inches (0.5 mm). The panel-formingsection 136 may be stretched at an average planar stretch ratio of about10.5:1, as described hereinafter. The planar stretch ratio is the ratioof the average thickness of the preform panel-forming portion 136 to theaverage thickness of the container panel (see for example sidewall 46 inFIG. 4), wherein the “average” is taken along the length of therespective preform or container portion. For refillable carbonatedbeverage bottles of about 0.5 to 2.0 liters in volume and about 0.5 to0.8 millimeters in panel wall thickness, a preferred planar stretchratio is about 7.5-10.5, and more preferably about 9.0-10.5. The hoopstretch is preferably about 3.2-3.5 and the axial stretch about 2.3-2.9.This produces a container panel with the desired abuse resistance, and apreform sidewall with the desired visual transparency. The specificpanel thickness and stretch ratio selected depend on the dimensions ofthe bottle, the internal pressure (e.g., 2 atmospheres for beer and 4atmospheres for soft drinks), and the processing characteristics (asdetermined for example, by the intrinsic viscosity of the particularmaterials employed).

[0066] In order to provide a thin PEN sleeve layer (e.g. 0.5 to 1.0 mm),a suitable mold cavity temperature would be on the order of 100 to 110°C. and core temperature of about 5 to 15° C., for a PET melt temperatureof about 285 to 295° C. and cycle time of about 6 to 7 seconds. Thefirst core set and warm inner layer are then immediately transferred tothe second station where the outer layers are injected and bondingoccurs between the inner and outer layers (e.g., exterior surface ofinner PEN sleeve layer at about 90 to 100° C. and innermost PET layer atabout 260 to 275° C.). The first core set and/or second cavity set atthe second station are cooled (e.g., about 5 to 15° C.) in order tosolidify the perform and enable removal from the mold. The cores andcavities at both the first and second stations include watercooling/heating passages for adjusting the temperature as desired.

[0067] In this embodiment, the inner sleeve layer 120 is made from ahigh-PEN copolymer having 90% PEN/10% PET by total weight of the layer,and in the container panel is about 0.004 inches (0.10 mm) thick. Theoutermost layer 123 is a virgin PET low copolymer having 3% comonomers(e.g., CHDM or IPA), and in the container panel is about 0.004 in (0.10mm) thick. The first intermediate layer 124 is PC-PET, and in thecontainer panel is about 0.012 in (0.30 mm) thick. The secondintermediate layer 125 is the same virgin PET low copolymer as outermostlayer 123, and in the container panel is about 0.002 in (0.05 mm) thick.The container shoulder and base (see 44 and 48 in FIG. 4A) are stretchedless and therefore are thicker and less oriented than the panel (see 46in FIG. 4A).

Fifth Preform Embodiment

[0068]FIG. 11 illustrates another preform embodiment for making arefillable carbonated beverage container. This preform has an additionaloutermost layer in the base only for increasing caustic stress crackresistance, while maximizing the use of post-consumer PET for reducingthe cost. The preform 160 includes an upper neck finish 162,shoulder-forming portion 164, panel-forming section 166, andbase-forming portion 168. The inner layer 170 has a body portion 171which is continuous throughout the length (including the bottom) of thepreform and includes an upper flange 172 forming the top sealingsurface. The inner layer is virgin PET. An outer layer 173 of PC-PETextends throughout the length of the preform, and forms a single outerlayer in the neck finish and panel-forming section. In the base-formingportion an additional exterior layer 174 of high IV virgin PET isprovided to enhance the caustic stress crack resistance of the blowncontainer. A thin interior layer 175 of the high IV virgin PET may alsobe formed according to the sequential injection process previouslyreferenced. A last shot 176 of high IV virgin PET is used to clear outthe PC-PET from the nozzle section. The outer base layer 174 ispreferably a high IV virgin PET (homopolymer or copolymer) having anintrinsic viscosity of at least about 0.76, and preferably in the rangeof 0.76 to 0.84. The resulting container may be either a footed orchampagne base container.

Sixth Preform Embodiment

[0069]FIG. 12 shows another preform embodiment including ahigh-temperature neck finish sleeve 190 and a single outer layer 194 forforming a hot-fill container. The preform 180 includes a neck finish182, shoulder-forming portion 184, panel-forming portion 186, andbase-forming portion 188. The inner sleeve 190 includes a neck finishportion 191, extending substantially along the length of the upperthreaded neck finish portion 182 of the container, and an upper flange192 forming a top sealing surface. The inner sleeve is formed of athermal resistant (high T_(g)) material such as a PEN homopolymer,copolymer or blend. Alternatively, the sleeve may be formed of CPET,sold by Eastman Chemical, Kingsport, Tenn, a polyethylene terephthalatepolymer with nucleating agents which cause the polymer to crystallizeduring the injection molding process.

[0070] The outer layer 194 is made of virgin PET. This preform isintended for making hot-fill containers, wherein the inner sleeve 190provides additional thermal stability at the neck finish.

[0071] In further alternative embodiments, a triple outer layer ofvirgin PET, PC-PET, and virgin PET may be used.

[0072] Alternative Constructions and Materials

[0073] There are numerous preform and container constructions, and manydifferent injection moldable materials, which may be adapted for aparticular food product and/or package, filling, and manufacturingprocess. Additional representative examples are given below.

[0074] Thermoplastic polymers useful in the present invention includepolyesters, polyamides and polycarbonates. Suitable polyesters includehomopolymers, copolymers or blends of polyethylene terephthalate (PET),polybutylene terephthalate (PBT), polypropylene terephthalate (PPT),polyethylene napthalate (PEN), and a cyclohexane dimethanol/PETcopolymer, known as PETG (available from Eastman Chemical, Kingsport,Tenn.). Suitable polyamides (PA) include PA6, PA6,6, PA6,4, PA6,10,PA11, PA12, etc. Other useful thermoplastic polymers includeacrylic/imide, amorphous nylon, polyacrylonitrile (PAN), polystyrene,crystallizable nylon (MXD-6), polyethylene (PE), polypropylene (PP), andpolyvinyl chloride (PVC).

[0075] Polyesters based on terephthalic or isophthalic acid arecommercially available and convenient. The hydroxy compounds aretypically ethylene glycol and 1,4-di-(hydroxy methyl)-cyclohexane. Theintrinsic viscosity for phthalate polyesters are typically in the rangeof 0.6 to 1.2, and more particularly 0.7 to 1.0 (for O-chlorolphenolsolvent). 0.6 corresponds approximately to a viscosity average molecularweight of 59,000, and 1.2 to a viscosity average molecular weight of112,000. In general, the phthalate polyester may include polymerlinkages, side chains, and end groups not related to the formalprecursors of a simple phthalate polyester previously specified.Conveniently, at least 90 mole percent will be terephthalic acid and atleast 90 mole percent an aliphatic glycol or glycols, especiallyethylene glycol.

[0076] Post-consumer PET (PC-PET) is a type of recycled PET preparedfrom PET plastic containers and other recyclables that are returned byconsumers for a recycling operation, and has now been approved by theFDA for use in certain food containers. PC-PET is known to have acertain level of I.V. (intrinsic viscosity), moisture content, andcontaminants. For example, typical PC-PET (having a flake size ofone-half inch maximum), has an I.V. average of about 0.66 dl/g, arelative humidity of less than 0.25%, and the following levels ofcontaminants:

[0077] PVC: <100 ppm

[0078] aluminum: <50 ppm

[0079] olefin polymers (HDPE, LDPE, PP): <500 ppm

[0080] paper and labels: <250 ppm

[0081] colored PET: <2000 ppm

[0082] other contaminants: <500 ppm

[0083] PC-PET may be used alone or in one or more layers for reducingthe cost or for other benefits.

[0084] Also useful as a base polymer or as a thermal resistant and/orhigh-oxygen barrier layer is a packaging material with physicalproperties similar to PET, namely polyethylene naphthalate (PEN). PENprovides a 3-5× improvement in barrier property and enhanced thermalresistance, at some additional expense. Polyethylene naphthalate (PEN)is a polyester produced when dimethyl 2,6-naphthalene dicarboxylate(NDC) is reacted with ethylene glycol. The PEN polymer comprisesrepeating units of ethylene 2,6 naphthalate. PEN resin is availablehaving an inherent viscosity of 0.67 dl/g and a molecular weight ofabout 20,000 from Amoco Chemical Company, Chicago, Ill. PEN has a glasstransition temperature T_(g) of about 123° C., and a melting temperatureT_(m) of about 267° C.

[0085] Oxygen barrier layers include ethylene/vinyl alcohol (EVOH), PEN,polyvinyl alcohol (PVOH), polyvinyldene chloride (PVDC), nylon 6,crystallizable nylon (MXD-6), LCP (liquid crystal polymer), amorphousnylon, polyacrylonitrile (PAN) and styrene acrylonitrile (SAN).

[0086] The intrinsic viscosity (I.V.) effects the processability of theresins. Polyethylene terephthalate having an intrinsic viscosity ofabout 0.8 is widely used in the carbonated soft drink (CSD) industry.Polyester resins for various applications may range from about 0.55 toabout 1.04, and more particularly from about 0.65 to 0.85dl/g. Intrinsicviscosity measurements of polyester resins are made according to theprocedure of ASTM D-2857, by employing 0.0050±0.0002 g/ml of the polymerin a solvent comprising o-chlorophenol (melting point 0° C.),respectively, at 30° C. Intrinsic viscosity (I.V.) is given by thefollowing formula:

I.V.=(ln(V _(Soln.) /V _(Sol.)))/C

[0087] where:

[0088] V_(Soln.) is the viscosity of the solution in any units;

[0089] V_(Sol.) is the viscosity of the solvent in the same units; and

[0090] C is the concentration in grams of polymer per 100 mls ofsolution.

[0091] The blown container body should be substantially transparent. Onemeasure of transparency is the percent haze for transmitted lightthrough the wall (H_(T)) which is given by the following formula:

H _(T) =[Y _(d)÷(Y _(d) +Y _(s))]×100

[0092] where Y_(d) is the diffuse light transmitted by the specimen, andY_(s) is the specular light transmitted by the specimen. The diffuse andspecular light transmission values are measured in accordance with ASTMMethod D 1003, using any standard color difference meter such as modelD25D3P manufactured by Hunterlab, Inc. The container body should have apercent haze (through the panel wall) of less than about 10%, and morepreferably less than about 5%.

[0093] The preform body-forming portion should also be substantiallyamorphous and transparent, having a percent haze across the wall of nomore than about 10%, and more preferably no more than about 5%.

[0094] The container will have varying levels of crystallinity atvarious positions along the height of the bottle from the neck finish tothe base. The percent crystallinity may be determined according to ASTM1505 as follows:

% crystallinity=[(ds−da)/(dc−da)]×100

[0095] where ds=sample density in g/cm³, da=density of an amorphous filmof zero percent crystallinity, and dc=density of the crystal calculatedfrom unit cell parameters. The panel portion of the container isstretched the greatest and preferably has an average percentcrystallinity in at least the outer layer of at least about 15%, andmore preferably at least about 20%. For primarily PET polymers, a 15-25%crystallinity range is useful in refill and hot-fill applications.

[0096] Further increases in crystallinity can be achieved by heatsetting to provide a combination of strain-induced and thermal-inducedcrystallization. Thermal-induced crystallinity is achieved at lowtemperatures to preserve transparency, e.g., holding the container incontact with a low temperature blow mold. In some applications, a highlevel of crystallinity at the surface of the sidewall alone issufficient.

[0097] As a further alternative embodiment, the preform may include oneor more layers of an oxygen scavenging material. Suitable oxygenscavenging materials are described in U.S. Ser. No. 08/355,703 filedDec. 14, 1994 by Collette et al., entitled “Oxygen ScavengingComposition For Multilayer Preform And Container,” which is herebyincorporated by reference in its entirety. As disclosed therein, theoxygen scavenger may be a metal-catalyzed oxidizable organic polymer,such as a polyamide, or an anti-oxidant such as phosphite or phenolic.The oxygen scavenger may be mixed with PC-PET to accelerate activationof the scavenger. The oxygen scavenger may be advantageously combinedwith other thermoplastic polymers to provide the desired injectionmolding and stretch blow molding characteristics for makingsubstantially amorphous injection molded preforms and substantiallytransparent biaxially oriented polyester containers. The oxygenscavenger may be provided as an interior layer to retard migration ofthe oxygen scavenger or its byproducts, and to prevent prematureactivation of the scavenger.

[0098] Refillable containers must fulfill several key performancecriteria in order to achieve commercial viability, including:

[0099] 1. high clarity (transparency) to permit visual on-lineinspection;

[0100] 2. dimensional stability over the life of the container; and

[0101] 3. resistance to caustic wash induced stress cracking andleakage.

[0102] Generally, a refillable plastic bottle must maintain itsfunctional and aesthetic characteristics over a minimum of 10 andpreferably 20 cycles or loops to be economically feasible. A cycle isgenerally comprised of (1) an empty hot caustic wash, (2) contaminantinspection (before and/or after wash) and product filling/capping, (3)warehouse storage, (4) distribution to wholesale and retail locationsand (5) purchase, use and empty storage by the consumer, followed byeventual return to the bottler.

[0103] A test procedure for simulating such a cycle would be as follows.As used in this specification and claims, the ability to withstand adesignated number of refill cycles without crack failure and/or with amaximum volume change is determined according to the following testprocedure.

[0104] Each container is subjected to a typical commercial caustic washsolution prepared with 3.5% sodium hydroxide by weight and tap water.The wash solution is maintained at a designated wash temperature, e.g.,60° C. The bottles are submerged uncapped in the wash for 15 minutes tosimulate the time/temperature conditions of a commercial bottle washsystem. After removal from the wash solution, the bottles are rinsed intap water and then filled with a carbonated water solution at 4.0±0.2atmospheres (to simulate the pressure in a carbonated soft drinkcontainer), capped and placed in a 38° C. convection oven at 50%relative humidity for 24 hours. This elevated oven temperature isselected to simulate longer commercial storage periods at lower ambienttemperatures. Upon removal from the oven, the containers are emptied andagain subjected to the same refill cycle, until failure.

[0105] A failure is defined as any crack propagating through the bottlewall which results in leakage and pressure loss. Volume change isdetermined by comparing the volume of liquid the container will hold atroom temperature, both before and after each refill cycle.

[0106] A refillable container can preferably withstand at least 20refill cycles at a wash temperature of 60° C. without failure, and withno more than 1.5% volume change after 20 cycles.

[0107] In this invention, a higher level of crystallization can beachieved in the neck finish compared to prior art processes whichcrystallize outside the mold. Thus, the preform neck finish may have alevel of crystallinity of at least about 30%. As a further example, aneck finish made of a PET homopolymer can be molded with an averagepercent crystallinity of at least about 35%, and more preferably atleast about 40% To facilitate bonding between the neck portion andbody-forming portion of the preform, one may use a thread split cavity,wherein the thread section of the mold is at a temperature above 60° C.,and preferably above 75° C.

[0108] As an additional benefit, a colored neck finish can be produced,while maintaining a transparent container body.

[0109] The neck portion can be monolayer or multilayer and made ofvarious polymers other than CPET, such as arylate polymers, polyethylenenaphthalate (PEN), polycarbonates, polypropylene, polyimides,polysulfones, acrylonitrile styrene, etc. As a further alternative, theneck portion can be made of a regular bottle-grade homopolymer or lowcopolymer PET (i.e., having a low crystallization rate), but thetemperature or other conditions of the first molding station can beadjusted to crystallize the neck portion.

[0110] Other benefits include the achievement of higher hot-filltemperatures (i.e., above 85° C.) because of the increased thermalresistance of the finish, and higher refill wash temperatures (i.e.,above 60° C.). The increased thermal resistance is also particularlyuseful in pasteurizable containers.

[0111] FIGS. 13A-13B illustrate graphically the change in melttemperature and orientation temperature for PET/PEN compositions, as theweight percent of PEN increases from 0 to 100. There are three classesof PET/PEN copolymers or blends: (a) a high-PEN concentration having onthe order of 80-100% PEN and 0-20% PET by total weight of the copolymeror blend, which is a strain-hardenable (orientable) and crystallizablematerial; (b) a mid-PEN. concentration having on the order of 20-80% PENand 80-20% PET, which is an amorphous non-crystallizable material thatwill not undergo strain hardening; and (c) a low-PEN concentrationhaving on the order of 1-20% PEN and 80-99% PET, which is acrystallizable and strain-hardenable material. A particular PEN/PETpolymer or blend can be selected from FIGS. 13A-13B based on theparticular application.

[0112]FIG. 14 illustrates a particular embodiment of a combined infrared(IR) and radio frequency (RF) heating system for reheating previouslymolded and cooled preforms (i.e., for use in a two-stage reheatinjection mold and stretch blow process). This system is intended forreheating preforms having layers with substantially differentorientation temperatures. For example, in the fourth preform embodimentthe high-PEN inner layer 120 has an orientation temperature much higherthan the virgin PET low copolymer and PC-PET outer layers 123-125. PENhomopolymer has a minimum orientation temperature on the order of 260°F. (127° C.), based on a glass transition temperature on the order of255° F. (123° C.). PEN homopolymer has a preferred orientation range ofabout 270-295° F. (132-146° C.). In contrast, PET homopolymer has aglass transition temperature on the order of 175° F. (80° C.). At theminimum orientation temperature of PEN homopolymer, PET homopolymerwould begin to crystallize and would no longer undergo strain hardening(orientation), and the resulting container would be opaque and haveinsufficient strength.

[0113] Returning to FIG. 14, this combined reheating apparatus may beused with preforms having a substantial disparity in orientationtemperatures between layers. The preforms 130 are held at the upper neckfinish by a collet 107 and travel along an endless chain 115 throughstations A, B and C in serial order. Station A is a radiant heating ovenin which the preforms are rotated while passing by a series of quartzheaters. The heating of each preform is primarily from the exteriorsurface and heat is transmitted across the wall to the inner layer. Theresulting heat or temperature profile is higher at the exterior surfaceof the preform than at the interior surface. The time and temperaturemay be adjusted in an attempt to equilibriate the temperature across thewall.

[0114] In this embodiment, it is desired to heat the inner PEN layer ata higher temperature because of PEN's higher orientation temperature.Thus, the preforms (across the wall) are brought up to an initialtemperature of about 160° F. (71° C.) at station A, and are thentransferred to station B which utilizes microwave or radio frequencyheaters. These high-frequency dielectric heaters provide a reversetemperature profile from that of the quartz heaters, with the interiorsurface of the preform being heated to a higher temperature than that ofthe exterior surface. FIG. 14 shows the preforms 130 traveling betweenelectrode plates 108 and 109, which are connected to RF generator 110and ground respectively. At station B, the inner layer is brought up toa temperature of about 295° F. (146° C.), and the outer layer to atemperature of about 200° F. (93° C.). Finally, the preforms are passedto station C, which is similar to station A. At station C the quartzheaters bring the preforms to a temperature of about 280° F. (138° C.)at the inner layer and about 210° F. (99° C.) at the outer layer. Thereheated preforms are then sent to a blow mold for stretch blow molding.A more detailed description of hybrid reheating of polyester preformsincluding a combination of quartz oven reheating and radio frequencyreheating is described in U.S. Pat. No. 4,731,513 to Collette entitled“Method Of Reheating Preforms For Forming Blow Molded Hot FillableContainers,” which issued Mar. 15, 1988, and is hereby incorporated byreference. In addition, additives may be provided in either or both ofthe PET and PEN layers to make them more receptive to radio frequencyheating.

[0115] In a preferred thin sleeve/thick outer layer embodiment, the thininner layer sleeve may have a thickness on the order of 0.02 to 0.06inch (0.5 to 1.5 mm), while the thick outer layer has a wall thicknesson the order of 0.10 to 0.25 inch (2.50 to 6.35 mm). The inner layer maycomprise on the order of 10-20% by total weight of the preform. Thisrepresents an improvement over the prior art single injection cavityprocess for making multilayer preforms. Also, the weight of one or moreouter layers (such as a layer of PC-PET) can be maximized.

[0116] While there have been shown and described several embodiments ofthe present invention, it will be obvious to those skilled in the artthat various changes and modifications may be made therein withoutdeparting from the scope of the invention as defined by the appendingclaims.

1. A method of injection molding a multilayer plastic articlecomprising: first molding an inner sleeve on a core positioned in afirst mold cavity; transferring the core and sleeve to a second moldcavity, while an outer surface of the sleeve is still at an elevatedtemperature from the first molding step, and second molding an outerlayer over the sleeve in a second mold cavity to form the multilayerinjection-molded plastic article, wherein temperatures of the firstcavity and core are selected to provide the elevated temperature at theouter surface of the inner sleeve sufficient to achieve melt adhesionbetween the inner sleeve and outer layer during the second molding step.2. The method of claim 1, wherein the melt adhesion between the innersleeve and outer layer includes diffusion bonding.
 3. The method ofclaim 1, wherein the melt adhesion between the inner sleeve and outerlayer includes chain entanglement.
 4. The method of claim 1, wherein thesleeve forms an upper sleeve portion of the article, and the outer layerforms a lower body portion of the article.
 5. The method of claim 4,wherein a lower end of the upper sleeve portion and an upper end of thelower body portion are joined in an intermediate portion of the article.6. The method of claim 1, wherein the first molding step forms the innersleeve as a full-length inner layer and upper surface of the article. 7.The method of claim 1, wherein the first molding step forms the innersleeve as an upper length portion of the article and an upper surface ofthe article.
 8. The method of claim 1, wherein the outer layer comprisesmultiple outer layers.
 9. The method of claim 1, wherein the article isa preform.
 10. The method of claim 9, wherein the first molding stepforms a neck finish portion of the preform.
 11. The method of claim 10,wherein the neck finish portion is molded from a polymer whichcrystallizes during the first molding step.
 12. The method of claim 9,wherein the neck finish portion is molded from a first polymer materialhaving a higher glass transition temperature than a second polymermaterial which forms the outer layer.
 13. The method of claim 1, whereinthe sleeve has a weight in a range on the order of 10 to 20 percent of atotal weight of the article.
 14. The method of claim 1, wherein thesleeve has a wall thickness in a range on the order of 0.02 to 0.06inch.
 15. The method of claim 14, wherein the outer layer has a wallthickness in a range on the order of 0.10 to 0.25 inch.
 16. The methodof claim 1, wherein the inner sleeve is formed of a first materialhaving a first melt temperature, and the outer layer includes a secondlayer adjacent the inner sleeve and made of a second material having asecond melt temperature lower than the first melt temperature.
 17. Themethod of claim 1, wherein the first mold cavity is at a first cavitytemperature and the second mold cavity is at a second cavity temperaturelower than the first cavity temperature.
 18. The method of claim 17,wherein the core is at a core temperature which is less than the firstcavity temperature.
 19. The method of claim 1, wherein the inner sleeveis formed of a first material having a first T_(g), and the elevatedtemperature is in a range on the order of 5-20° C. below the firstT_(g).
 20. The method of claim 1, wherein the sleeve is molded from afirst material selected from the group consisting of homopolymers,copolymers, and blends of polyethylene naphthalate (PEN).
 21. The methodof claim 1, wherein the outer layer includes at least one layer moldedfrom a second material selected from the group consisting ofpolyethylene terephthalate (PET), an oxygen scavenging material,recycled PET, polyethylene, polypropylene, polyacrylate, polycarbonate,polyacrylonitrile, nylon, and copolymers and blends thereof.
 22. Themethod of claim 1, wherein the article has a sidewall portion in whichthe inner sleeve has a relatively thin first thickness (t₁) and theouter layer has a relatively thick second thickness (t₂), and the ratioof t₂:t₁ is greater than on the order of 4:1.
 23. The method of claim 1,wherein the article has a relatively thin first thickness (t₁) and theouter layer has a relatively thick second thickness (t₂), and the ratioof t₂:t₁ is on the order of from 1.2:1 to 8:1.
 24. The method of claim1, wherein the inner sleeve is substantially crystallized and the outerlayer is substantially amorphous.
 25. The method of claim 1, wherein theinner sleeve is made of a first material and the outer layer is made ofa second material, and the second material has a relatively lowcrystallization rate compared to the first material.
 26. The method ofclaim 1, wherein first and second cores are provided, and wherein duringa first cycle the first core is positioned in the first mold cavity toform a first inner sleeve, and the second core, having a second innersleeve positioned thereon, is simultaneously positioned in the secondmold cavity for molding a second outer layer on the second inner sleeve.27. The method of claim 26, wherein the first and second cores aresuccessively transferred between the first and second mold cavities. 28.The method of claim 1, wherein the sleeve is molded of a first materialselected from the group consisting of polyester, polyester withnucleating agents, acrylate, polyethylene naphthalate (PEN),polycarbonate, polypropylene, polyamide, polysulfone, acrylonitrilestyrene, and copolymers and blends thereof.
 29. The method of claim 28,wherein the outer layer includes a second material selected from thegroup consisting of homopolymers, copolymers, and blends of any one ormore of: polyethylene terephthalate (PET), polyethylene naphthalate(PEN), and recycled PET.
 30. The method of claim 1, wherein the articlehas a body portion and the method further comprises expanding the bodyportion of the article to form an expanded article having asubstantially transparent and biaxially-oriented body portion.
 31. Themethod of claim 1, wherein the method further comprises cooling thearticle below a first glass transition temperature of a first materialin the article, reheating the article above the first glass transitiontemperature, and expanding the reheated article to form an expandedarticle.
 32. The method of claim 31, wherein the expanded article has ahigh T_(g) or crystallized upper neck finish portion and a substantiallytransparent, biaxially-oriented body portion.
 33. An apparatus formaking multilayer injection-molded plastic articles comprising: at leastone set of first and second mold cavities, each first cavity beingadapted to form a relatively thin inner sleeve and each second cavitybeing adapted to form a relatively thick outer layer; a transfermechanism having at least one set of first and second cores, forsuccessively positioning the first and second core sets in the first andsecond cavity sets; and wherein the first core set is positionable inthe first cavity set for molding a first set of inner sleeves on thefirst core set, while the second core set is positionable in the secondcavity set for molding, over a previously-molded set of first innersleeves on the second core set, a second set of outer layers.
 34. Theapparatus of claim 33, wherein the first cavity and core define a firstwall thickness (t₁) and the second cavity and core define a second wallthickness (t₂), and wherein a ratio of t₂:t₁ is greater than on theorder of 4:1.
 35. The apparatus of claim 33, wherein the transfermechanism is a rotatable turret.
 36. The apparatus of claim 33, whereinthe transfer mechanism is a reciprocating shuttle.
 37. An apparatus formaking multilayer injection-molded plastic articles comprising: at leastone set of first and second mold cavities, each first cavity beingadapted to form an inner sleeve and each second cavity being adapted toform a multilayer outer layer; a transfer mechanism having at least oneset of first and second cores, for successively positioning the firstand second core sets in the first and second cavity sets; and whereinthe first core set is positionable in the first cavity set for molding afirst set of inner sleeves on the first core set, while the second coreset is positionable in the second cavity set for molding, over apreviously-molded set of first inner sleeves on the second core set, asecond set of multilayer outer layers.
 38. A method of injection moldinga plastic preform comprising: injection molding a first thermoplasticmaterial to form a first preform portion having an average percentcrystallinity of at least about 30%; and injection molding a secondthermoplastic material to form a second preform portion which remainssubstantially amorphous.
 39. The method of claim 38, wherein the firstportion is substantially a neck portion and the second portion issubstantially a body-forming portion.
 40. The method of claim 38,wherein the second material has a relatively low crystallization ratecompared to the first material.
 41. The method of claim 40, wherein thefirst material is selected from the group consisting of polyester,polyester with nucleating agents, arylate polymers, polyethylenenaphthalate (PEN), polycarbonate, polypropylene, polyamide, polysulfone,acrylonitrile styrene, and copolymers and blends thereof.
 42. The methodof claim 41, wherein the second material is selected from the groupconsisting of homopolymers, copolymers and blends of any one or more of:polyethylene terephthalate (PET), polyethylene naphthalate (PEN), andrecycled PET.
 43. The method of claim 41, further comprising expandingthe second portion to form a substantially transparent andbiaxially-oriented body of a container.
 44. A method of injectionmolding a multilayer plastic article comprising: first molding an innersleeve on a core positioned in a first mold cavity, wherein the core isrelatively cooler and the first cavity is relatively warmer and thefirst molding step includes a filling stage and a pressure boost stagebut substantially no holding and cooling stage; removing the sleeve onthe core and transferring the same without substantial delay to a secondmolding cavity; and second molding an outer layer over the sleeve in thesecond mold cavity, to form the multilayer injection molded article. 45.The method of claim 1, wherein the inner sleeve is made of a PEN polymermaterial and the elevated temperature is in a range on the order of60-120° C.
 46. The method of claim 45, wherein the first molding stephas a cycle time on the order of no greater than 8 seconds.
 47. Themethod of claim 45, wherein the cycle time is in a range on the order of4-8 seconds.
 48. The method of claim 45, wherein the first cavitytemperature is in a range on the order of 40-120° C. and the coretemperature is in a range on the order of 5-80° C.
 49. The method ofclaim 48, wherein the first cavity temperature is in a range on theorder of 75-95° C. and the core temperature is in a range on the orderof 60-70° C.
 50. The method of claim 48, wherein the first cavitytemperature is in a range on the order of 100-110° C. and the coretemperature is in a range on the order of 5-15° C.
 51. The method ofclaim 48, wherein the PEN polymer material has a melt temperature in arange on the order of 275-295° C. and the elevated temperature is in arange on the order of 90-110° C.
 52. The method of claim 45, wherein theouter layer includes a PET polymer material adjacent the inner sleeve,the PET polymer material having a melt temperature in a range on theorder of 260-275° C. and the second molding step being carried out at acavity pressure in a range on the order of 8000-15,000 psi.
 53. Themethod of claim 1, wherein the inner sleeve is made of a polyesterpolymer material which is crystallized during the first molding step andthe elevated temperature is in a range on the order of 80-140° C. 54.The method of claim 53, wherein the first molding step has a cycle timeon the order of no greater than 8 seconds.
 55. The method of claim 54,wherein the cycle time is in a range on the order of 5-8 seconds. 56.The method of claim 53, wherein the first cavity temperature is in arange on the order of 80-150° C. and the core temperature is in a rangeon the order of 5-60° C.
 57. The method of claim 56, wherein the firstcavity temperature is in a range on the order of 110-120° C. and thecore temperature is in a range on the order of 5-15° C.
 58. The methodof claim 53, wherein the polyester polymer material has a melttemperature in a range on the order of 280-290° C. and the elevatedtemperature is in a range on the order of 115-125° C.
 59. The method ofclaim 53, wherein the outer layer includes a PET polymer materialadjacent the inner sleeve, the PET polymer material having a melttemperature in a range on the order of 270-285° C. and the secondmolding step being carried out at a cavity pressure in a range on theorder of 8000-15,000 psi.
 60. A method of injection molding a multilayerplastic article comprising: first molding an inner sleeve of a PENpolymer material on a core positioned in a first mold cavity, the firstholding step including a filling stage and a pressure boost stage butsubstantially no holding and cooling stage; transferring the core andsleeve without substantial delay to a second mold cavity, while an outersurface of the sleeve is at an elevated temperature in a range on theorder of 100-110° C., and second molding an outer layer of a PET polymermaterial over the sleeve in a second mold cavity to form the multilayerinjection-molded plastic article, wherein the PET polymer material has amelt temperature in a range on the order of 260-275° C. and the secondmolding step is carried out at a cavity pressure in a range on the orderof 8000-15,000 psi to achieve melt adhesion between the inner sleeve andouter layer during the second molding step.
 61. A method of injectionmolding a multilayer plastic article comprising: first molding an innersleeve of a PEN polymer material on a core positioned in a first moldcavity, the first molding step including a filling stage and a pressureboost stage but substantially no holding and cooling stage; transferringthe core and sleeve without substantial delay to a second mold cavity,while an outer surface of the sleeve is at an elevated temperature in arange on the order of 90-100° C., and second molding an outer layer of aPET polymer material over the sleeve in a second mold cavity to form themultilayer injection-molded plastic article, wherein the PET polymermaterial has a melt temperature in a range on the order of 260-275° C.and the second molding step is carried out at a cavity pressure in arange on the order of 8000-15,000 psi to achieve melt adhesion betweenthe inner sleeve and outer layer during the second molding step.
 62. Amethod of injection molding a multilayer plastic article comprising:first molding an inner sleeve of a polyester polymer material which iscrystallized on a core positioned in a first mold cavity, the firstmolding step including a filling stage and a pressure boost stage butsubstantially no holding and cooling stage; transferring the core andsleeve without substantial delay to a second mold cavity, while an outersurface of the sleeve is at an elevated temperature in a range on theorder of 115-125° C., and second molding an outer layer of a PET polymermaterial over the sleeve in a second mold cavity to form the multilayerinjection-molded plastic article, wherein the PET polymer material has amelt temperature in a range on the order of 270-285° C. and the secondmolding step is carried out at a cavity presure in a range on the orderof 8000-15,000 psi to achieve melt adhesion between the inner sleeve andouter layer during the second molding step.